Horse sacrifices were performed by powerful rulers. It was about the enlargement of the kingdom and about one’s own fame. A horse was released and the regent of any realm that it entered had to submit to or fight against the owner of the horse.
Only Indra had made a hundred horse sacrifices. He was always on the lookout that no worldly king surpassed him.
When King Sagara planned the hundredth horse sacrifice Indra intervened.
The story is part of the Ganga myth
When King Dilipa planned the hundredth horse sacrifice a compromise was found.